Electrical insulating composition and process of making the same.



UNITED STATES, PATENT OFFICE- "WILLIAM H. STEINBEBG, OF 'MILWAUKEE, WISCONSIN, ASSIGNOR TO THE CUTLER- HAMM EB'MFG. 00., OF MILWAUKEE, WISCONSIN, A CORPORATION OF WISCONSIN.

'nnric'rnicnn INSULATING COMPOSITION AND PROCESS or Maxine THE SAME.

1,233,416. Ho Drawing.

To all whom it may concern: Be it known that 1,. WILLIAM H. STEIN-- BERG, a citizen of the United States,:residing at Milwaukee, in the county of Milwaukee and State of Wisconsin, have invented new and useful Improvements in Electrical In-' composition of material particularly adapted for electrical insulating purposes.

In my prior application Serial No. 11,337, filed March 1, 1915, there is disclosed a composition having a base including comminuted asbestos and sulfur and-a binder including coal tar pitch, stearin pitch, castor oil and benzol and also a method of combining, the aforesaid ingredients I This composition has proven a great success commercially and'the present invention contemplates the use of the same ingredients and their equivalents but the combination thereof in a slightly different way to further increase the utility of the product.

More particularly the former method provided for cold mixing of the castor oil with a preheated mixture of the two pitches and while the resultantproduct was readily molda'ble in innumerable forms it exhibited a tendency to crack when molded in certain special forms and the present invention eliminates, or at least greatly minimizes, such tendency and powibly improves the product in other respects not yet ascertained.

Accordin to the present invention coinminuted'as tos is employed for the base and sulfur is added thereto as in the com position mentioned, the sulfur constituting what is believed to be a vulcanizing agent in the final product. The asbestos and sul fur may, of course, be used in the desired proportions but in practice it has been found advantageous to use an amount of sulfur l fllequal to two percent. of the weight of the asbestos: Theasbestoe and sulfur are mixed dry rior to the addition of the binder.

A so, as in the aforesaid composition, the binder includes coal tar pitch and stearin 9 pitch, preferably in equal parts, which are mixed in thepresence of heat from &00 to 500 F. until the free carbon thereof preci itates. Then while said pitches are heat- 0 an animal or vegetable oil capable of vulcanization or polymerization, preferably Specification of Letters Patent. Patented J 1y 1'7, 191'1 Application filed August 23, 1915. Serial No. 46,976.

castor oil, is added thereto in the proportion of 10% of the combined weight ofthe pitches I after precipitation of the carbon, although as will be understood these proportions may bevai'ied, if desired. Then after the addi- .60

t ion offthe aforesaid oil the supernatant liquid is drawn off and cooled and a volatile solvent, preferably benzol, added thereto,

' which completes the binder. The percentage of benzol may, of course, be varied but an amount equal to 50% of the'liquid to which it is added is usually sufiicient- Thus whereas in the formation of the binder of the former composition the benzol and castor oil were added to the supernatant 7 liquid after cooling, the castor oil is now added before the benzol and while the pitches are still heated. Moreover, with the binder so formed, it is found that the tendency for the composition to crack when ni'olded is materially minimized, if not entirelyeliinii ated, while the castor oil still functions as in the former binder tostabilize the benzol, or in other words, reduce the rate of free volatilization thereof. theory of the improved result cannot be advanced with certainty it seems probable that the tendency of the former composition to crack resulted from the/extreme grcasiness of the castor oil'and that by the present 3 method the effect thereof is neutralized.

After the base and binder are completed they are mixed in a cold state as described in my prior application, preferably in the While the 0 proportions of four parts of the base to one part of the binder and when mixed thor-- oughly they produce a granular but plastic compound. This compound maythen be molded without heat and subsequently baked to produce an extremely hard and dense insulation. In molding, the material is preferably subjected to a pressure'of 6,000 to 10,000 pounds per square inch and in baking the molded article is preferably subjected to a gradually increasing heat up to 450 01" 500 F. and for a period of AP roximately twenty-four hours. AS in the. minor composition the baking drives of? by evaporation the ingredients which uIQ V0 atllo at the pre vailing temperatures and during the baking the sulfur and the CY StOI oil and otlie hemicull v unsatisfied constitm-n't:-; of the binder combine or vnlmnizo to yield A tough and durable insulating produi-r. which will resist heat to at least 450 to 500 F. Without I softening or distorting. Also, as in the former composition, the precipitation of the free carbon of the fectiveness-of the blnder, as set forth in my prior application, aforesaid.

lVhatI claim as new and desire to-secure by Letters Patent is 1. A' binder for the purpose set forth, in-

' cl uding coal tar pitch, stearin pitch and an forth including a base with a: vulcanizing or polymerizing agent oil capable ofvulcanization or polymerization all mixed in the presence of heat.

2. A binder for the purpose set forth including a preheated mixture of coal tar pitch, stearin pitch and an oil capable of vulcanization with a volatile solvent. composition of the character set having mixed thereand a binder for said base including a preheated cpm'binatio'n of coal tarpitch, stearin pitch and an oil capable of vulcanization or polymerization.

4. A composition of the character set forth including comminuted asbestos and sulfur and a -binder composed of a preheated combination of coal tar fpitch, stearin pitch and an oil capable o pitches augments the ef- ,in combining under heat in combining under heat coal or polymerization combined- .in combining ujider heat 'stearin pitchv until. the free carbon thereof is precipitated, then combining therewith] vulcanization or polymerization mixed with a volatile sol- 5. The; herein described method consisting vent.

in combining under .heat coal tar pitch, stearin pitch and an 01]. capable of vulcanization or polymerization.

6. The herein described method consisting coal tar pitch, stearin pitch and an oil capable of vulcanization or therewith when cooled a volatile solvent.

7. The herein described method consisting tar pitch and stearin pitch until the free carbon thereof is precipitated and then combining there.-

with under. heat'an oil capable of Vulcanization or polymerization.

8., The herein described method consisting coal tar pitch and under heat an oilcapable of vulcanization or polymerization and then cooling the resultant product and adding thereto a volatile solvent,

polymerization and then mixing In wands whereof, I have hereunto'subscribed, my name.

WILLIAM H. STEINBERG. 

